The present invention relates to a method and an apparatus for adjusting the print positions of a dot line printer.
A method and an apparatus for adjusting the print positions of a dot line printer in the prior art will be described in detail with reference to the drawings.
FIG. 1 is a perspective view for explaining a first prior-art example (refer to, for example, Japanese Unexamined Patent Publication (JP-A) No. 244282/1996).
The dot line printer is constructed of a hammer bank 2 in which a large number of printing hammers 1 are arrayed in one row, a shuttle mechanism 8 which vibrates the hammer bank 2 laterally at a predetermined amplitude, a sheet feed mechanism 12, and so forth.
In the shuffle mechanism 8, the hammer bank 2 supported by right and left parallel flat springs 7 is connected to an eccentric cam 6 of a shuttle drive motor 5 through a connecting rod 4. When the shuttle drive motor 5 is rotated, the hammer bank 2 is vibrated in an approximate sinusoidal wave rightwards and leftwards. The sheet feed mechanism 12 is constituted by a platen 9 for transporting a printing sheet 13, and a sheet feed motor 11 for driving the platen 9 through a belt 10, thereby to transport the sheet 13 every dot line very exactly. While the hammer bank 2 is vibrated, the respective printing hammers 1 are operated to print dots at predetermined intervals, so that one row of dots is formed by the one-way operation (forward printing) Subsequently, when the hammer bank 2 is turned back (for reverse printing), the sheet 13 is transported the interval of one dot line, and the next dot line is printed. Further, the sheet 13 is transported one dot line immediately before forward printing. Characters are printed by repeating such operations. Incidentally, numeral 3 designates an inking ribbon.
FIG. 2 is a waveform diagram showing the printing timing signals of the prior-art dot line printer. A hammer bank leftmost-end signal 30 and a hammer bank rightmost-end signal 31 indicating the arrivals of the hammer bank 2 at the leftmost end and rightmost end thereof start a forward printing timing signal 32 for executing the forward printing and a reverse printing timing signal 33 for executing the reverse printing, respectively. Both the forward printing timing signal 32 and the reverse printing timing signal 33 are generated substantially at the time when hammer bank speed 36 is a set value. Since the printing is performed by reciprocally moving the hammer bank 2 by means of the shuttle mechanism 8, the printing of the identical printing hammer 1 must not allow a misalignment or shear between the lateral printing of the forward printing mode and that of the reverse printing mode. It is difficult, however, to avoid the lateral print shear of the identical printing hammer 1 between the forward and reverse printing modes merely by keeping the mechanical balance of the shuttle mechanism 8 which reciprocally moves the hammer bank 2. In the prior-art dot line printer, therefore, a reverse printing timing signal 35 as shown in FIG. 2 is generated after a delay of a time period after the transmission of the pulse of the hammer bank rightmost-end signal 31. The printing of the identical printing hammer 1 can be freed from the lateral print shear between in the forward printing mode and in the reverse printing mode by adjusting the time period t.
Besides, the line feed of the dot line of the sheet 13 is started by the final pulse of both the forward printing timing signal 34 and the reverse printing timing signal 35.
With the method for adjusting the print positions of the dot line printer in the first prior-art example, it is intended to compensate for the lateral print shear of the identical printing hammer 1 by shifting the reverse printing timing signal 35 in the reciprocal motion. On the other hand, the sheet line feed operation is started by the final pulse of both the forward printing timing signal 34 and the reverse printing timing signal 35, so that decrease or increase in the time period of the line feed is incurred. Accordingly, the sheet 13 does not cease moving before the start of the printing as shown by the sheet line feed speed 37 in FIG. 2, and hence, print dot positions become disordered to degrade print quality.
FIG. 3 is a waveform diagram showing a second prior-art example. Here in the second prior-art example, a dot line printer itself is supposed the same as shown in FIG. 1. A hammer bank leftmost-end signal 20 and a hammer bank rightmost-end signal 21 indicating the arrivals of the hammer bank 2 at the leftmost end and rightmost end thereof start a forward printing timing signal 22 for executing the forward printing and a reverse printing timing signal 23 for executing the reverse printing, respectively. Both the forward printing timing signal 22 and the reverse printing timing signal 23 are substantially generated at times when hammer bank speed 26 is a predetermined value.
Since the printing is performed by reciprocally moving the hammer bank 2 by means of the shuttle mechanism 8, in the printing of the identical printing hammer 1 shear or misalignment between the lateral print of the forward printing mode and that of the reverse printing mode is not allowable. It is difficult, however, to avoid the lateral print shear of the identical printing hammer 1 between in the forward printing mode and in the reverse printing mode merely by keeping the mechanical balance of the shuttle mechanism 8 which reciprocally moves the hammer bank 2.
Therefore, a forward printing timing signal 24 as shown in FIG. 3 is generated after a delay of a time period t1 following generation of the pulse of the hammer bank leftmost-end signal 20.
Subsequently, a reverse printing timing signal 25 as shown in FIG. 3 is generated after a delay of a time period t2 following generation of the pulse of the hammer bank rightmost-end signal 21. The printing of the identical printing hammer 1 can be freed from the lateral print shear between the forward printing mode and the reverse printing mode by adjusting the time periods t1 and t2.
The line feed of the dot line of the sheet 13 is started by the final pulse of both the forward printing timing signal 24 and the reverse printing timing signal 25. In this embodiment, the forward printing timing signal 24 and the reverse printing timing signal 25 are both adjusted by the predetermined adjustment time periods t1 and t2 relatively to the hammer bank leftmost-end signal 20 and the hammer bank rightmost-end signal 21, respectively. As shown by a sheet line feed speed 27 in FIG. 3, therefore, decrease or increase in the time period of the line feed is not incurred, to eliminate the drawback that the sheet 13 does not come to a stop before the start of the printing, causing print dot positions to become disordered to degrade print quality. Further, the adjustment can be facilitated more by equalizing the adjustment time periods t1 and t2.
With the method and apparatus for adjusting the print positions of the dot line printer in the second prior-art example, only one printing element assembly is concerned, and hence, the print shear can be avoided by adjusting the forward and reverse printing timing signals. However, in a case where a dot line printer includes a plurality of printing element assemblies and where the relative positions of the printing element assemblies in the extending direction thereof (in the line direction of a printing sheet) are not exactly in alignment, the relative positions of the print dots of the printing element assemblies cannot be corrected merely by the pair of printing timing signals in the forward and reverse modes.
Further, even in case of a known dot line printer whose printing mechanism module has a plurality of printing element assemblies, only one drive circuit is included, and only one printing timing signal is generated by a control circuit. Besides, while the printing element assemblies are mechanically coupled, the relative positions of these printing element assemblies in the extending direction thereof sometimes fail to meet designed values on account of discrepancy in the dimensions of the individual printing element assemblies. On this occasion, since only one printing timing signal is generated, the positions of installed printing elements are directly reflected on print dots formed, and the relative positions between the print dots in the extending direction (in the line direction of a printing sheet) fall outside designed values.
In a case where the relative positions between the print dots in the line direction misalign by a large amount due to the plurality of printing element assemblies, these assemblies must be mechanically regulated, and the magnitude of the regulation is a level of several tens xcexcm. Accordingly, there have hitherto been the disadvantages that the regulation is difficult and that the number of the stages of the adjusting work enlarges.
It is therefore an object of the present invention to provide a method and an apparatus for adjusting the print positions of a dot line printer according to which the relative positions between print dots in the line direction of a printing sheet can be brought to appropriate relative positions without performing any mechanical regulation.
Another object of the present invention to provide a method and an apparatus for adjusting the print positions of a dot line printer according to which the number of the stages of adjusting work is small.
According to the present invention, in a dot line printer having a printing mechanism module which includes a plurality of printing element assemblies each having at least one printing element and which are mechanically coupled, and there is provided a method for adjusting print positions of the dot line printer characterized the adjustment steps of assigning drive circuits to the respective printing element assemblies, and generating a plurality of printing timing signals and individually sending them to said respective printing element assemblies by means of a control circuit, thereby to compensate a misalignment of relative positions between print dots of the printing element assemblies in opposing directions of printing, the misalignment being attendant upon a misalignment of relative positions between the printing element assemblies in opposing line directions.
Also, according to the present invention, in a dot line printer having a printing mechanism module which includes a plurality of printing element assemblies each having at least one printing element and which are mechanically coupled, there is provided an apparatus for adjusting print positions of the dot line printer, characterized by adjustment means for assigning drive circuits to the respective printing element assemblies, and generating a plurality of printing timing signals and individually sending them to the respective printing element assemblies by means of a control circuit, thereby to compensate a misalignment of relative positions between print dots of the printing element assemblies in opposing directions of printing, the misalignment being attendant upon a misalignment of relative positions between the printing element assemblies in opposing line directions.
Further, according to the present invention, in a dot line printer having a printing mechanism module which includes a plurality of printing element assemblies each having at least one printing element and which are mechanically coupled, there is provided an apparatus for adjusting print positions of the dot fine printer, characterized by comprising a detector which detects a position of the printing mechanism module, and a control circuit which generates two sorts of printing timing signals on the basis of an output signal of the detector.